Excerpted from an article over at the NYT...
“You have several options, as I see it, when you become aware of someone else’s antipathy,” said Melissa Witkow, now at Willamette University in Oregon, the psychologist who led the study. “You could be extra nice, and that might be good. But it could also be awkward or disappointing, and a waste of time. You could choose to ignore the person. Or you can engage.”
She said the study suggested that “when someone dislikes you, it may be adaptive to dislike them back.”
One reason may be that people tend to prefer symmetry in their relationships, balance in their shared antagonism just as in their shared affection. Growing up is in large part an exercise in self-definition. From a very early age, psychoanalysts have long argued, children develop objects of hatred onto which they can project the traits in themselves that they find most offensive.
The same is true of groups: a shared enemy enhances cohesion and a sense of self-approval. In psychology jargon, focusing on so-called out-group members can strengthen bonds among members of a clique.